As a safety component of great importance for elevators, buffers for elevators are generally arranged at the bottom of a stroke of an elevator cage and a counterweight device. When an elevator goes beyond the bottom floor or the top floor, the cage or counterweight hits against the buffer which absorbs or consumes the kinetic energy of the elevator, such that the cage or counterweight is slowed down safely until stops. The buffers for elevators are divided in two main forms: energy storage buffers and energy dissipation buffers (also called hydraulic buffers). The energy storage buffers are only suitable for elevators with speed below 1 m/s, while the hydraulic buffers are suitable for any type of elevators. In addition, under the same usage conditions, the stroke required by the hydraulic buffers is half that of the spring buffers, so that the personal and equipment are better protected during operation of the evaluator. Hence, passenger elevators generally use hydraulic buffers. Hidden risks can be found in advance through routine maintenance and detection of buffers, thus ensuring the reliable operation of hydraulic buffers, which is crucial to the safety of elevators.
The safety performance of the hydraulic buffers will be influenced by various factors such as the length of compression stroke, the reposition time and whether jamming occurs during reposition. It is required in the Regulation for Lift Supervisory Inspection and Periodical Inspection—Traction and Positive Drive Lift (TSG7001-2009) that before an elevator is put into use after installation, an inspection and detection mechanism for special equipment should be used to perform confirmatory supervision and inspection to the working conditions of the hydraulic buffers; and that the maximum time limit for the complete reposition of the hydraulic buffers is 120 s (the reposition time is a time measured from the lifting of the cage to the reposition of the buffer to an original state after the buffer is completely compressed). At present, during the detection of the reposition time of a buffer for an elevator, if a person observes the timing in a pit which has a poor environment and is also dangerous, the visual inspection and manual timing are subjective. Considering the personal safety of the inspector, if the inspector monitors the compression of the cage (counterweight) to the buffer outside the cage or in a machine room, and then times the reposition process of the buffer, it is more difficult to accurately judge when the case is lifted, when the buffer repositions to the original state, and how long the actual compression stroke of the buffer is.
Conventional ways for measuring the reposition of a hydraulic buffer still depend on manual operation. Dynamic characteristics of “complete compression” and “the moment when the cage is lifted” required by the regulation can only be determined subjectively, thus no quick, reliable and accurate measurement of related data can be carried out, resulting in various problems such as large human factors in the measurement of the reposition time of the buffer, low measurement accuracy, high dispersion of results, and low detection efficiency. Due to the problems of large measurement difficulty and low measurement accuracy, the detection fails to reflect the safety performance of the buffer timely and comprehensively and thus cannot effectively ensure the safe operation of the elevators. Besides, if the inspector does not squat in a pit (it is very dangerous for the inspector to squat in the pit to make observations when the buffer is completely compressed), the inspector is unable to measure the actual compression stroke of the buffer, and thus unable to know whether jamming occurs during compression and reposition of the buffer.